Various and numerous sulfonated and otherwise derived lignin materials have already been found, known and developed and advantageously applied for many useful and beneficial purposes. This includes the alkaline oxidized, partially desulfonated lignosulfonates of the type prepared according to the teachings and disclosures of U.S. Pat. No. 2,491,832 which are prepared from treatments of alkaline sulfite waste pulping liquor from wood conversion.
While numerous references are available dealing in one capacity or discipline or another with the identity and nature of lignin, per se, and many of the derivatives of lignin including lignosulfonates (all of which, by the way, are generally relatively imprecise and not positively definite), preparation and multitudinous uses of the contemplated materials, substantial elucidation thereupon and thereof may also be found, by way of illustration, in U.S. Pat. Nos. 1,848,292; 2,371,136; 2,371,137; 2,505,304; 2,576,418; 2,598,311; 2,800,449; 3,156,520; and 3,726,850. Still additional art of interest is uncovered in U.S. Pat. Nos. Re. 18,268; 2,057,117; 2,104,701; 2,399,607; and 2,434,626.
Another excellent informational source in this area is the Bulletin (No. 131) published by AMERICAN CAN COMPANY of Greenwich, Conn., 06830 (U.S.A.) entitled "Chemicals From Wood".
The alkaline oxidized, hydrolyzed, partially desulfonated lignosulfonates which are utilized as the starting materials in practice of and to obtain the novel resulfonated compositions of the present invention are, as indicated, usually most readily and conveniently obtained pursuant to the teachings of U.S. Pat. No. 2,491,832. In this process, especially if and when enhanced by-product yields of vanillin are wanted, it is frequently more desirable to employ a waste pulping liquor for the process which is derived from a totally, or at least substantially, softwood source -- although this is not an entirely restrictive limitation since hardwood starting materials can, of necessity, also be used.
Using the patented process, the degree of desulfonation realized is a factor of and controlled by the amount of caustic interjected for the reaction; the strength of the oxidation effected (i.e., the relative amount of air or oxygen employed -- although the oxidation conditions cannot be so severe as to induce demethylation consequences); the reaction times and temperatures schedules followed, and the solids dilution, generally aqueous, of the lignosulfonate-containing spent sulfite liquor effluent being treated (with greater dilution conditions tending to lead to more extensive desulfonation probably due to the thereby increased availability of the reacting molecules to the oxidizing influence applied).
While very desirable partially desulfonated lignosulfonate materials are prepared with the alkaline oxidation conducted on a spent sulfite liquor containing, on a weight percent basis, from about 30 to 35% of dissolved solids, the spent liquors being cooked in the desulfonation process may have as little as 14-10% to as much as 40% solids content in order to obtain beneficial desulfonated products.
Practically, almost any caustic alkaline solution can be employed for effecting the partial desulfonation reaction, although lower alkalinity generally results in less desulfonation. More caustic is required when sugars and other saccharides are present (and they are usually present with otherwise untreated spent sulfite liquors) in any varied or more substantial amounts in order to effect the decomposition of such saccharides. Ordinarily, very good results are achieved when sufficient caustic concentration is maintained throughout the desulfonating cook to maintain the reaction mass in the relatively high pH range of between about 10.5 and about 11. For example, a quite satisfactory proportion of lignosulfonate solids to caustic to employ in the reaction mass involves use of an aqueous lignosulfonate solution of about 31-32 wt.% and having a specific gravity around 1.22-1.24 or so containing a caustic concentration in the solution of about 140 gms. NaOH/liter.
Adequate oxidation conditions to achieve desired ranges of desulfonation of the lignosulfonate in the spent sulfite liquor may be achieved by providing, almost invariably from either air or oxygen passed through the cooking reaction mass, between about 20-25 or so and about 40-50 or so grams of elemental oxygen (i.e., O.sub.2) per each 100 grams of lignin in the lignosulfonate material being desulfonated. In actual practice to obtain a frequently more desirable range of partially desulfonated material, between about 27 and 35 grams of O.sub.2 per gram of lignin are utilized.
While variations may be encountered, temperatures on the range of from about 140.degree. to about 170.degree. C., advantageously in the neighborhood of 165.degree. C., are usually most desirable to utilize. Of course, the reacting mass is cooked until the desired degree of desulfonation (or, when vanallin by-product is important, the desired yield of it) is obtained. Usually and at the 165.degree. C. level the cooking time is on the order of 45 minutes or so; the optimum time to employ, as will be appreciated by those skilled in the art, depending on reaction conditions and the particular degree of desulfonation desired in the resulting partially desulfonated lignosulfonate material. It is oftentimes most advantageous (if not literally necessary for material handling purposes) to terminate the cooking while some free caustic still remains in the reaction mass. This tends to prevent problems of emulsification during subsequent recovery of the partially desulfonated lignosulfonate. Beneficially and for the indicated purpose, the reaction may accordingly be finished when, say, about 4-5 gms./liter of free NaOH is found to remain in the reaction mass.
Practice of the process of U.S. Pat. No. 2,491,832 yields, in effect, a spent oxidized liquor which, as has been disclosed and as is known, contains partially desulfonated, generally acid-insoluble, chemically altered organic lignin substances. These are usually isolated and/or fractionated by acid (namely, sulfuric) precipitation which eliminates various sludge-producing, mostly calcium-based, ingredients therein. After the precipation, the purified partially desulfonated lignosulfonate material is generally dissolved in caustic to yield a sodium salt; then spray or otherwise dried to yield a powder product--although, if desired, it may be finally prepared and used in an undried liquified form or reconstituted to an aqueous liquid of any desired concentration.
The partially desulfonated lignosulfonate material thus obtained is not directly procurable from original spent sulfite liquors as are the normally-gotten and ordinarily so-called, albeit undesulfonated, "lignosulfonatess; " it being an exceptionally pure material containing essentially no sugars or polysaccharides; having only vanishing traces, if any, of combined sulfur in sulfite form; and also having other inherent distinguishing features including relatively uniform and substantially constant relative molecular size characteristics.
Although a sugar and saccharide-containing spent sulfite liquor is desirable to employ as the starting material for preparation of partially desulfonated lignosulfonates from which the resulfonated compositions of the present invention are derived, otherwise treated spent sulfite liquors may equivalently be utilized. These, for example, may be those which have previously been treated in divergent ways and for other initial conversion purposes wherein the sugars and/or saccharides are utilized and consumed, as in the preliminary manufacture from raw spent sulfite liquor of yeast or alcohol or in other ways giving a sugar and/or saccharide -reduced or -free spent sulfite liquor.
The alkaline oxidized, partially desulfonated lignosulfonates which are aninonic polyelectrolytes with a relative molecular size usually on the order of 1,000 to 20,000 and from which the resulfonated products are obtained according to the instant invention generally have an organic sulfonic sulfur, i.e., --SO.sub.3, content calculated as percent sulfur by weight of broadly between about 1/2 and about 5 wt. %. More advantageously for many purposes, this sulfur range is between about 13/4 and about 33/4 wt. %; while quite often it is preferable for the partially desulfonated lignosulfonate to contain from about 2.2 to about 2.8 wt. % of the combined sulfur which represents its appearance in the sulfonic form.
A commercially available product, "MARASPERSE CB" (.TM.) obtainable from AMERICAN CAN COMPANY, is a good example of an excellent alkaline oxidized, hydrolyzed, partially desulfonated lignosulfonate material useful in practice of the present invention.
"MARASPERSE CB, " as usually available, generally has the following typical analysis parameters and physical characteristics features:
______________________________________ TYPICAL ANALYSES (Moisture-Free and Wt. % Basis): pH - 3% Solution 8.5-9.2 Total Sulfur as S, % 2.5-2.9 Sulfate Sulfur as S, % 0.1-0.25 Sulfite Sulfur as S, % 0-0.05 CaO, % 0.02-0.05 MgO, % Trace-0.03 Na.sub.2 O, % 9.4-9.9 Reducing sugars, % 0 OCH.sub.3, % 12.4-12.9 Sodium Lignosulfonate, % 99-99.6 Solids, % 92-94 ULTRAVIOLET ANALYSES (K-value representing base line) Upper UV: K Solids at Max. (275 mu) 29-30.5 K OCH.sub.3 at Max. 225-250 Differential UV: Max. nm 250-252 K Solids at Max. 10-11.3 K OCH.sub.3 at Max. 82-88 Baseline K Solids 9.5-10.5 Phenolic OH, % 1.8-2.1 OH/OCH.sub.3 0.26-0.30 PHYSICAL CHARACTERISTICS Usual Form Powder Moisture Content (Max., % H.sub.2 O) 8.0 Color Black Bulk Density (lbs./cu. ft.) 43-47 Solubility in Water (%) 100 Solubility in Oils and Most Organic Solvents (%) 0 Surface Tension, 1% Sol'n (in dynes/cm) ca. 51.4 ______________________________________
While the known alkaline oxidized, hydrolyzed, partially desulfonated lignosulfonates, including such things as "MARASPERSE CB, " are excellent surfactant, dispersant, detergent and otherwise attractively-propertied materials very good for a wide variety of uses, they still have certain intrinsic inadequacies and limitations leaving some desiderata and unfulfilled capacbility for use in many crucial applications and for expanded applicability in and for many highly advantageous purposes. Noteworthy amongst these are difficulties in the employment of the mentioned partial desulfonated lignosulfonates are their relatively limited solubility in saline solutions plus their sometimes not totally satisfactory potential for having extraordinarily superb general surfactant exhibitions.